Patterning of Small Particles Surface Tension vs Temperature

Patterning of Small Particles & Surface Tension vs. Temperature Lu Zou Group meeting Jul. 10, ’ 06 Ref: Nguyen, V. X. ; Stebe, K. J. ; PRL, Vol. 88, 164501, 2002 07/10/06 Group Meeting 1

Patterning of Nanoparticles n n A drop containing finely divided particles Evaporation Particles are deposited in macroscopic patterns Interactions among the particles can be exploited to create local order 07/10/06 Group Meeting 2

“Coffee Ring” & “Benard Cells” n R. D. Deegan and others 1997. "Capillary flow as the cause of ring stains from dried liquid drops", Nature, volume 389, pp 827 -829 07/10/06 Group Meeting n n M. Maillard, L. Motte, M. -P. Pileni ; Rings and Hexagons Made of Nanocrystals, Adv. Mater. 2001, 13, 200 -204 (or say, periodic flow patterns, Hexagon patterns) 3

Why a drying drop forms a “Coffee Ring”? Ref: http: //mrsec. uchicago. edu/ Nuggets/Coffee/ 07/10/06 Group Meeting 4

Benard Convection physics. ucsd. edu/was-daedalus/ convection/rb. html 07/10/06 Group Meeting 5

A Droplet with Surfactant Pentadecanoic Acid (PDA) HCl + 0. 01% microspheres (D = 0. 8 um) Dyed by NBD-HDA Modified Si. O 2 Substrate Contact angle for water is 50 o +/- 3 o 07/10/06 Group Meeting 6

Isotherm of PDA w/ NBD-HDA 07/10/06 Group Meeting 7

For the LC-LE State 07/10/06 Group Meeting 8

For the LE State When the interface is in LCLE coexistence, the Benard convection is present, even though the concentration of the surfactant is significant. 07/10/06 Group Meeting 9

2 Possible Explanation n In the LE-LC coexistence regime, compositional Marangoni stresses are weak. n In the LE-LC coexistence regime, temperature-driven Marangoni stresses are strong. 07/10/06 Group Meeting 10